Study of Monsoon Onset Variability and Its Effects on Crop Planting in Kebbi State

The West African monsoon is the primary driver of rainfall seasonality across the Sudan Savanna and Sahel belts of northern Nigeria, and its inter-annual variability has profound consequences for agricultural planning. This study examines the variability of monsoon onset dates over Kebbi State and assesses the downstream effects on crop planting decisions among smallholder farmers. Daily rainfall records from NiMet synoptic stations in Birnin Kebbi and Argungu for the period 2012 to 2023 were analyzed using the PRESAO criterion for monsoon onset determination. Focus group discussions and household surveys involving 180 farming households in Gwandu and Augie LGAs provided qualitative and quantitative data on farmer adaptation to onset variability. Results demonstrate that monsoon onset in Kebbi State has exhibited inter-annual variability of plus or minus 18 days relative to the long-term mean of 5 May. Years with late monsoon onset (after 25 May) are significantly correlated with reduced millet and cowpea yields, with early planting false starts increasing input losses in approximately 35 percent of sampled households. The study finds that farmers primarily rely on traditional ecological knowledge for planting decisions, with limited use of NiMet seasonal forecasts. Recommendations include development of locally customized monsoon onset forecast bulletins disseminated through community radio and mobile SMS platforms. Keywords: monsoon onset, Kebbi, planting date, crop yield, West African monsoon.